This invention relates electric lamps and more particularly to such lamps having non-rotatable bases.
There are several known techniques for securing a screw base onto a lamp outer jacket. The latter generally takes the form of a glass bulb. One conventional method is to mold a threaded area on the lower or base portion of the outer jacket glass so that a screw base can be threaded thereon. During the formation of the threads an indentation also is made near the top thereof. When the lamp is being completed, one of the in-lead wires of the lamp is pressed into a lead solder slug and the lead solder slug is inserted into the indentation. The base is threaded onto the lamp over the lead solder slug, heat is applied, and the solder joint is completed. This operation electrically connects one of the lamp in-leads to the base and mechanically holds the base onto the glass bulb of the outer jacket. A significant problem with this basing technique is that the lead solder can pose an environmental problem when the lamp is disposed of, as well as creating a manufacturing hazard during the production of the lamp.
Recently, other techniques have been proposed to alleviate the hazards in the use of the lead solder. Among these techniques are those shown in U.S. Pat. Nos. 5,381,070 and 5,521,460 (these two patents being assigned to the assignee of the instant invention) and 5,550,422. While all of these approaches solved the problem of lead solder usage, they introduced other concerns.
For example, the solution represented by U.S. Pat. No. 5,550,422 has the undesirable requirement that the base clip must be physically attached to the lamp by snapping it onto the bottom seal of the lamp. This provides an additional step in the manufacturing process. Further, the clip is attached to an area of the glass that is normally more fragile. The area at the bottom can have sharper angles and residual stress that make the area susceptible to glass fracture. By attaching the clip to this area, glass fractures can occur both during lamp manufacture or when the lamp is being extracted from a tight socket.
The methods shown in U.S. Pat. Nos. 5,381,070 and 5,521,460 avoid these problems by making the mechanical and electrical connection through a clip that is not attached to the bottom seal of the lamp. However, a disadvantage of these two designs is that the clip has sharp edges. These sharp edges are in contact with the glass in the area where the base is mechanically secured to the lamp. When a torque is applied to the base, for example, during extraction from a socket, the sharp edges impinge on the glass and place a high-localized pressure on the glass. This pressure can achieve levels that are sufficient to fracture the glass. This is an undesired potential failure mode because the lamp jacket can separate from the base, leaving a base with sharp glass fragments in the socket. It is also possible that such a failure mode will expose the lamp electrical circuit, thus creating the risk of an electrical shock.
Another issue occurring with the designs of U.S. Pat. Nos. 5,381,070 and 5,521,460 is that they can create an outward protrusion that extends outwardly past the base shell by more than 0.050 inches, a distance that exceeds ANSI specifications. The outward extension of the clips of these patents has a straight portion that is normally bent over the base shell during the basing operation, typically forming a radius at the clip-to-shell interface. This radius, also, can often be too large and form a protrusion that is beyond the ANSI specification.
A solution to the above-cited problems is shown in U.S. application Ser. No.: 09/357,027, still pending filed Jul. 20, 1999, and assigned to the assignee of the present invention. Therein, a locking clip is provided for fixing a base to an end of a glass bulb. The locking clip comprises a body having a first portion, a middle portion and an end portion, with the middle portion being scyphate and defining a plane. The first portion extends away from the plane in a given direction by an angle of about 5 degrees. The end portion is connected to the middle portion by a reentrant section and extends away from the plane in a direction opposite the given direction by an angle of about 20 degrees. The scyphate middle portion extends the full width of the clip and thus provides only softly curving surfaces in contact with a groove in the glass. This design works extremely well with leaded Nonex glass, eliminating the lead solder slug and controlling the outward extension within ANSI limits. However, when applied to the newest lamp designs, which utilize lead-free glass to eliminate problems associated with the manufacture and disposal of lead containing glass, it has been discovered that the base-clip attachment was not adequate, since the lamps could not pass a routine torque testing without cracking the envelope.
It is, therefore, an object of this invention to obviate the disadvantages of the prior art.
It is another object of the invention to enhance the base-to-clip junction of lamps.
Yet another object of the invention is the provision of base-to-clip junction that reduces stresses in the lamp.
Still another object of the invention is a lead-free lamp that will not fracture easily during removal from a tight socket.
These objects are accomplished, in one aspect of the invention, by a lamp that comprises an electrically insulating, light-transmitting, lead-free envelope having a base end and containing a light source. At least two electrical lead-ins are connected to the light source and exit the envelope. A base is affixed to the base end, the base comprising first and second electrically conductive portions separated by an electrically insulating portion. One of the electrical lead-ins is electrically connected to the first electrically conductive portion and another of the electrically conductive lead-ins is electrically connected to the second electrically conductive portion. The base is non-rotationally mounted to the base end by a locking clip affixed to the first electrically conductive portion by mechanical means and affixed to the base by chemical means.